Author Topic: Converting a triple 9spd crankset to a single for SRAM NX 12  (Read 1208 times)

Converting a triple 9spd crankset to a single for SRAM NX 12
« on: 18 February, 2020, 07:01:26 pm »
I'm trying to source a chainring for my crankset, a Shimano Hollowtech 2 XT FC-M771 triple. I want to completely remove the existing chainrings (replace the existing 48 Tooth 9-Speed Chainring 104 BCD) and fit a chainring which is 12spd compatible, have heard an 11spd chainring would also suffice. It seems that the manufacturers concentrate on the smaller sizes for the MTB market. The only place I've found which seems to have a big selection is SJS cycles.

But the problem is I've no idea if any of these will fit ???  How on earth do you nail down what is compatible? Is it a case of matching the BCD from the same manufacturer?

Re: Converting a triple 9spd crankset to a single for SRAM NX 12
« Reply #1 on: 18 February, 2020, 07:12:06 pm »
The internal width of 9/10/11/12 speed chains is the same so the my widen your choice.
We are making a New World (Paul Nash, 1918)

Re: Converting a triple 9spd crankset to a single for SRAM NX 12
« Reply #2 on: 18 February, 2020, 09:46:10 pm »
The internal width of 9/10/11/12 speed chains is the same so the my widen your choice.

Thank you, also had a look here and it's beginning to make sense. Since I'm only going to have a single up front it looks like I'll get away with it. The only other spanner in the works would be the length of the links but they look to be the same  :thumbsup:

Re: Converting a triple 9spd crankset to a single for SRAM NX 12
« Reply #3 on: 05 March, 2020, 09:56:42 pm »
The 12 speed chain will be fine on any 3/32 chainring. Search on eBay for a 104bcd narrow wide ring.

Mike

Re: Converting a triple 9spd crankset to a single for SRAM NX 12
« Reply #4 on: 05 March, 2020, 10:57:20 pm »
'any 3/32" chainring' includes ones which were meant originally for 5/6s systems.  A 9-12s chain (which is referred to by the manufacturers as 11/128" chain not 3/32" chain) will be snug on those teeth; the slightest bit of mud, or burring of the teeth and chainsuck is quite likely.

cheers

Re: Converting a triple 9spd crankset to a single for SRAM NX 12
« Reply #5 on: 06 March, 2020, 10:48:20 pm »
'any 3/32" chainring' includes ones which were meant originally for 5/6s systems.  A 9-12s chain (which is referred to by the manufacturers as 11/128" chain not 3/32" chain) will be snug on those teeth; the slightest bit of mud, or burring of the teeth and chainsuck is quite likely.

cheers

That's cool to know - I've never seen a label suggesting 11/128th, but equally I've never bothered converting from the metric either.

Re: Converting a triple 9spd crankset to a single for SRAM NX 12
« Reply #6 on: 07 March, 2020, 12:08:59 am »
11/128" is how KMC refer to their 10s etc chains. It is an accurate indication of the internal width of the chain.  In practice you need lateral clearance from the sides of the teeth to the chain. The amount of clearance you need varies depending on

- 1x,2x or 3x
- singlespeed or derailleur
- if muddy conditions are likely
- if burring of the teeth is likely.

A few years ago I built a bike up using an old set of triple chainrings and a 9s chain.  I nearly drove myself berserk trying to get the chain to downshift off the middle chainring. I eventually concluded that the chain was just too snug on the teeth of the chainring; a different chain transformed it out of all recognition. 1/128" clearance evidently made a difference!

cheers

cheers

Re: Converting a triple 9spd crankset to a single for SRAM NX 12
« Reply #7 on: 07 March, 2020, 12:43:54 am »
Though the cheapo narrow wide 104 BCD chainrings referred to upthread are universally labelled 9-12 speed rather than their width in smoots.

What width chain they actually work with varies by whatever manufacturing tolerances they felt like using that day. One of mine needed some mild weight reduction to make it work with an 11 speed chain.

Re: Converting a triple 9spd crankset to a single for SRAM NX 12
« Reply #8 on: 07 March, 2020, 09:49:07 am »
NW chainrings have an additional issue which is that the thicker teeth also have scallops in them (or are otherwise shaped) to clear the inner sideplates where they protrude into the outer side-plate  half-link.  Some NW chainrings are fussier than others about what chain works with them than others.  I suspect that the width of the wide teeth may also vary between makes in NW chainrings (so an 11s NW chainring ought to have slightly narrower wide teeth than a 10s one), but I have not measured them.

cheers